Pediatric hearing loss (PHL) is a risk factor for poor spoken language development and educational outcomes. Positive language outcomes may depend in large part on the linguistic environment. Because infants with PHL are at risk for poor language outcomes, the quality of the input may be even more important for them than it is for infants with normal hearing (NH). However, there is currently very little known about the nature of the linguistic input to infants with hearing loss and how it affects their language development. The overall objective of this research project is to determine how real-world language input affects language development in infants with hearing loss and to determine the underlying factors of infant-directed speech (IDS) that might facilitate language development in these infants. In Aim 1, we will measure and compare the acoustic and linguistic- pragmatic properties of real-world speech directed to infants with PHL and NH peers using the LENA recording device. In Aim 2, we will investigate relationships between properties of real-world IDS and outcome measures and determine the role of infants' processing efficiency on mediating those relationships. In Aim 3, we will determine the effects of IDS on novel word learning in infants with PHL compared to NH peers. The Babytalk Research Laboratory at Indiana University School of Medicine employs an established intermodal preferential looking paradigm for studying novel word learning in both NH infants and infants with PHL. In this procedure, infants are seated in a sound booth and are presented with auditory and visual signals on a TV monitor. Infants' looking times to the target and nontarget visual objects in response to the novel words - spoken in either infant-directed or adult-directed speech registers - will be measured as an index of their word learning ability. Finally, in Aim 4, we will determine which acoustic characteristics of IDS facilitate novel word learning in NH infants under conditions of natural and spectrally degraded speech. Using the same novel-word-learning paradigm as in Aim 3, this specific aim will be the first to investigate the facilitative effects of specific acoustic propertes of IDS on novel word learning in NH infants and will provide valuable information regarding how spectrally degraded speech may affect the facilitative affects of IDS. The findings from this research project will have important theoretical implications because they will shed light on how PHL and spectrally degraded input interacts with the direct and indirect relationships between IDS and language development. The findings will also provide valuable information to clinicians and parents of infants with hearing loss for providing an optimal linguistic environment that will best promote language development.